An apparatus for generating engine intake air turbulence is proposed. In order to suppress the pressure loss in the maximum valve opening degree, it is avoided to use a butterfly valve for a turbulence generator valve. Instead, a cantilever valve or a rotary valve is used as a turbulence generator valve. For example, JP4556864B (US2007144483A1) discloses one.
Since the butterfly valve usually has a rotatable shaft on a center of a movable valve member, it is possible to reduce rotating torque caused by an intake air flow. Hereinafter, the rotating torque caused by the intake air flow may be referred to as an intake flow torque TA. However, the rotary valve may receives larger intake flow torque TA, since the rotary valve is un rotating torque (intake flow torque TA is asymmetrical about a rotatable shaft.
As a concrete example, in a case of a cantilever valve, an intake flow torque TA becomes the maximum when the valve is fully closed, 0% of a valve opening degree (VD), and becomes the minimum when the valve is fully opened, 100% of VD. An example is shown in FIG. 2.